Euryhaline

Abstract: Oxygen-deficient and H2S-containing marine areas are characterized by a decline in the number of species. In laboratory experiments with bottom invertebrates from various biotopes of the North Sea and the Baltic, comparative measurements of the resistance to oxygen-deficiency alone, and to the simultaneous presence of H2S, were carried out. The resistance values obtained show relations to the substratum on which the species naturally occur. The resistance to H2S is greater in those macrofauna species which show higher survival rates under oxygen-deficiency. Further experiments with isolated tissues demonstrate that the species specific differences in resistance occurring in whole animals are already based on the cell metabolism. In general, oxygen-deficiency and simultaneous presence of H2S were endured better in cold than in warmth, and at somewhat reduced pH-values (around 7). The dependence of this resistance on the salinity was only minimal in euryhaline species.

Abstract: Toxic Pfiesteria-like dinoflagellates have been implicated as causative agents of major fish kills (affecting 10 3 -10 9 fish) in estuaries and coastal waters of the mid-Atlantic and southeastern US Transformations among an array of flagellated, amoeboid, and encysted stages in the complex life cycle of the representative species, Pfiesteria piscicida, are controlled by the availability of fresh secretions, blood, or other tissues of fish prey P piscicida also is a voracious predator on other estuarine microorganisms Pfiesteria-like dinoflagellates require an unidentified substance(s) commonly found in fresh fish excreta-secreta to initiate toxin production P piscicida is lethal to fish at low cell densities (>250-300 cells ml -1 ), and at sublethal levels (∼100-250 cells ml-') it has been shown to cause ulcerative fish diseases P piscicida also has been linked to serious human health impacts This dinoflagellate is eurythermal and euryhaline, with optima for toxic activity by the most lethal stage (toxic zoospores, TZs) at ≥26°C and 15 psu, respectively Thus far it has shown no light optimum and is capable of killing fish at any time during a 24-h cycle In warmer waters (≥15°C) flagellated stages predominate while fish are dying, whereas amoebae predominate in colder conditions and when fish are dead Nutritional stimuli influencing P piscicida are complex; inorganic phosphate apparently can directly stimulate TZs, whereas inorganic phosphate and nitrate indirectly promote increased production of nontoxic zoospores (NTZs, maintained in the absence of live fish, as potential precursors to lethal TZs) by stimulating their algal prey Organic phosphate (P o ) and nitrogen are taken up by P piscicida osmotrophically, and P o is stimulatory to both TZs and NTZs The available data point to a critical need to characterize the chronic and acute impacts of toxic Pfiesteria-like dinoflagellates on fish and other targeted prey in estuarine and coastal waters that are adversely affected by cultural eutrophication

Abstract: Salinity represents a critical environmental factor for all aquatic organisms, including fishes. Environments of stable salinity are inhabited by stenohaline fishes having narrow salinity tolerance ranges. Environments of variable salinity are inhabited by euryhaline fishes having wide salinity tolerance ranges. Euryhaline fishes harbor mechanisms that control dynamic changes in osmoregulatory strategy from active salt absorption to salt secretion and from water excretion to water retention. These mechanisms of dynamic control of osmoregulatory strategy include the ability to perceive changes in environmental salinity that perturb body water and salt homeostasis (osmosensing), signaling networks that encode information about the direction and magnitude of salinity change, and epithelial transport and permeability effectors. These mechanisms of euryhalinity likely arose by mosaic evolution involving ancestral and derived protein functions. Most proteins necessary for euryhalinity are also critical for other biological functions and are preserved even in stenohaline fish. Only a few proteins have evolved functions specific to euryhaline fish and they may vary in different fish taxa because of multiple independent phylogenetic origins of euryhalinity in fish. Moreover, proteins involved in combinatorial osmosensing are likely interchangeable. Most euryhaline fishes have an upper salinity tolerance limit of approximately 2× seawater (60 g kg −1 ). However, some species tolerate up to 130 g kg −1 salinity and they may be able to do so by switching their adaptive strategy when the salinity exceeds 60 g kg −1 . The superior salinity stress tolerance of euryhaline fishes represents an evolutionary advantage favoring their expansion and adaptive radiation in a climate of rapidly changing and pulsatory fluctuating salinity. Because such a climate scenario has been predicted, it is intriguing to mechanistically understand euryhalinity and how this complex physiological phenotype evolves under high selection pressure.